1. Field of the Invention
The present invention relates to a method for waterproofing a power circuit section including a bus bar and a semiconductor device and disposed on a heat radiating member via an insulating layer, and more particularly to a method for waterproofing a power circuit section for distributing electric power from a common in-vehicle power source to a plurality of electronic units, and a power module having the power circuit section.
2. Description of the Related Art
Conventionally, as means for distributing electric power from the common in-vehicle power source to the plurality of electronic units, an electrical connection box is well-known in which a plurality of bus bar boards are laminated to constitute the power circuit section and into which a fuse and a relay switch are incorporated.
Generally, such electrical connection box has the power circuit section accommodated within a case including an upper case and a lower case. From a viewpoint of preventing the short-circuit, the lower case and the upper case are fitted together water-tightly to waterproof the inside of the case.
In recent years, in order to miniaturize the electrical connection box and realize high-speed switching control, a power module has been developed in which a semiconductor switching device such as FET is interposed between an input terminal and an output terminal, instead of the relay. From a viewpoint of cooling a heat generated by the semiconductor device, a power module has been proposed in which the power circuit section is disposed via an insulating layer on a circuit disposition surface of the heat radiating member (e.g., JP-A-11-204700).
In such power module, a method for forming an external connection terminal connected to an external circuit includes bending up an end portion of a bus bar provided in the power circuit section disposed on the circuit disposition surface to form the external connection terminal connected to an external connector. However, in this structure, the connecting direction is limited to the normal direction to the circuit disposition surface. Thus, to make the connecting direction parallel to the circuit disposition surface, it is conceived to extend the end portion of the bus bar straightly from the power circuit section. However, in this case, the external connection terminal is located near the circuit disposition surface of the heat radiating member, bringing about a danger of causing a short-circuit when there is a large current or a large voltage, even though the external connection terminal and the heat radiating member are separated apart. Also, there is a problem that a proper insulation between the external connection terminal and the heat radiating member is not secured when they make contact with each other temporarily due to vibration. Also, when the external connection terminal is disposed near the circuit disposition surface of the heat radiating member, there is another problem that it is difficult to form a connector by surrounding the external connection terminal with the hood.
On the other hand, in the above power module, it is necessary to prevent the short-circuit, as in the conventional electrical connection box. Accordingly, though it is required to waterproof its circuit section, no specific method of waterproofing has been disclosed.